Parasitism by blood-feeding horn flies, Haematobia irritans (L.), exacts a toll on cattle health and well being that results in economic losses estimated to approach $1 billion in North America alone (Cupp et al., 1998). In addition to the direct physiological impact of their feeding on cattle, horn flies are known to transmit the bovine filarial parasite, Stephanofilaria stilesi (Hibler, 1966) and the causative agent of bovine mastitis, Staphylococcus aureus (Owens et al., 2002, 1998). The benefits of horn fly control for promoting animal health and productivity have been demonstrated using presently available chemical means (Derouen et al., 2009, Sanson et al, 2003, Guglielmone et al., 1999).
Classical methods of chemical control, however, typically lead to selection for insecticide resistance that can severely limit the lifetime of any particular formulation. These complications of insecticidal use highlight the need to find other, more specific and long lasting, means of disrupting H. irritans parasitism of cattle (Oyarzim et al., 2008). Basic studies of horn fly blood-feeding revealed the importance of salivary proteins in fly-cattle interactions that lead to successful parasitism (Cupp et al., 1998). These studies identified a dominant thrombin-inhibiting protein, thrombostasin (TS), in horn fly saliva and implicated it as a key factor in successful blood-feeding by this important ectoparasite of cattle (Cupp et al., 2000).
Thus, there remains a need for agents capable of reducing the deleterious effect of the horn fly on susceptible populations.